Emissions regulations which must be met by vehicles are becoming increasingly strict. In order to meet these increasingly strict regulations, it is felt that, in the future, something other than a conventional internal combustion engine vehicle will be required.
One suggestion that might meet this requirement is a hybrid vehicle which is powered by a combination of an internal combustion engine and an electric motor. An additional factor motivating the use of hybrid vehicles is the suggested zero emission zone which might be used in city centres to reduce acute urban pollution. A hybrid vehicle could meet the requirements of the zero emission zone within the city and yet still have sufficient acceleration and range to allow its use outside urban areas.
Having designed a hybrid vehicle, there is a need to establish the way in which the powertrain of the vehicle should be used. The term "powertrain" means the engine and drive transmission by means of which power is transmitted to drive the vehicle. Under some circumstances, one method of operating the powertrain will be obvious. For instance, when a hybrid vehicle is used for a long motorway journey, the electric part of the powertrain will be unable to make a useful contribution because of the amount of power and energy required. Conversely, in a zero emission zone, the internal combustion engine can make no contribution. However, there are potentially two other ways in which the powertrain of the vehicle could be used. The power for propelling the vehicle could be drawn partly from the internal combustion engine and partly from the electric motor. That would have the advantage of being less emissive and cheaper than using the internal combustion engine alone. A further method might be to use the electric motor to oppose the internal combustion engine of the vehicle, in order to increase the state of charge of the battery used to power the electric motor. That might be useful when approaching a zero emission zone with a depleted battery.
The first two categories mentioned above will not require any large increase in complexity since the drive arrangements will be similar to those of conventional internal combustion engine vehicles and electric vehicles respectively. The second two methods of operation will require the separate actions of the engine and the electric motor to be combined and one object of the present invention is to provide a suitable controller for that purpose so that the driver does not have to control the electric motor and the engine individually.